It is known to incorporate inorganic particulate fillers, such as ground inorganic minerals into polymer compositions for a variety of purposes. Approaches have been proposed to improve the compatibility of the inorganic filler and the polymer composition. For example, U.S. Pat. No. 7,732,514 describes a composition comprising a plastics material, an inorganic particulate solid such as aluminium hydrate and a coupling surface modifier. In coupling surface modifiers the modifier interacts with both the surface of the particulate filler and the polymer matrix.
In recent years, the recycling of polymer waste material has come to the fore. However, the recycling of polymer waste material has presented challenges which are not necessarily encountered during the preparation of polymer compositions derived from virgin polymer.
These challenges include the problem of contamination and soiling of the polymer waste resulting from its original use and during post-use collection and initial processing. Such contamination can be in the form of volatile and/or solid impurities. The presence of such contaminants imparts unpleasant odours to the polymer waste material and, if not properly removed, can adversely affect the quality of the final recycled polymer. Typically, polymer waste is treated in a single washing step to remove contaminants.
Further, polymer waste streams often comprise a mixture of different polymer types, e.g., polyethylene and polypropylene, which can present compatibility problems in recycled polymers prepared from such mixed polymer waste streams. Conventionally, therefore, greater focus is placed on the separation of polymers into their constituent types before further processing. However, such separation is technically arduous and therefore relatively expensive.
Thus, as the need to recycle polymer waste materials increases, there is a continuing need for the development of new methods and compositions for the economically viable processing of polymer waste materials into high quality polymer compositions and articles.
The present inventors have found new fillers for use in polymer compositions, particularly polymer compositions derived from post-consumer polymer waste, as well as new processes for recycling polymer waste materials, which address or at least ameliorate the aforementioned problems and which also enable the production of low odour, high quality recycled polymer compositions.